The present invention is in the field of imaging systems. More particularly, the present invention provides an apparatus and method for picking printing plates of various sizes.
In external drum imaging systems, a movable optical carriage is commonly used to displace an image exposing or recording source in a slow scan direction while a cylindrical drum supporting recording media on an external surface thereof is rotated with respect to the image exposing source. The drum rotation causes the recording media to advance past the exposing source along a direction which is substantially perpendicular to the slow scan direction. The recording media is therefore advanced past the exposing source by the rotating drum in a fast scan direction.
An image exposing source may include an optical system for scanning one or more exposing or recording beams. Each recording beam may be separately modulated according to a digital information signal representing data corresponding to the image to be recorded.
The recording media to be imaged by an external drum imaging system is commonly supplied in discrete, flexible sheets and may comprise a plurality of plates, hereinafter collectively referred to as xe2x80x9cplatesxe2x80x9d or xe2x80x9cprinting plates.xe2x80x9d Each printing plate may comprise one or more layers supported by a support substrate, which for many printing plates is a plano-graphic aluminum sheet or a polyester support. Other layers may include one or more image recording (i.e., xe2x80x9cimageablexe2x80x9d) layers such as a photosensitive, radiation sensitive, or thermally sensitive layer, or other chemically or physically alterable layers. Printing plates are available in a wide variety of sizes, typically ranging, e.g., from 9xe2x80x3xc3x9712xe2x80x3, or smaller, to 58xe2x80x3xc3x9780xe2x80x3, or larger.
A vacuum system, comprising a plurality of suction cups coupled to a vacuum source, is often employed to lift, or xe2x80x9cpick,xe2x80x9d the top printing plate from a stack of printing plates, prior to the top printing plated being fed to the external drum of an imaging system. One cost-effective method of simultaneously distributing a vacuum to the plurality of suction cups involves the use of a single venturi vacuum pump. An example of such a vacuum system 10 is illustrated in FIG. 1. In particular, the vacuum system 10 includes a vacuum pump 12 for generating a vacuum, a plurality of suction cups 14A-14F, tubing 16, and identical, non-constricted (i.e., xe2x80x9cstraight-throughxe2x80x9d) fittings 22 for coupling the suction cups 14A-14F in parallel to the vacuum pump 12 via tubing 16. In this configuration, a vacuum provided by the vacuum pump 12 is simultaneously applied and distributed to each of the plurality of suction cups 14A-14F.
As depicted in FIG. 2, the vacuum system 10 may be used to pick the top printing plate 18 off of a stack 20 of printing plates. When the top printing plate 18 has a width Wp greater than the effective width WSC of the plurality of suction cups 14A-14F sufficient vacuum is available at each of the suction cups 14A-14F to allow the top printing plate 18 to be lifted from the stack 20 of printing plates.
Problems may occur, however, when the vacuum system 10 is used to pick up a printing plate 18 having a width WP substantially narrower than the effective width WSC of the plurality of suction cups 14A-14F. For example, as shown in FIG. 3, only two of the suction cups (i.e., suction cups 14C and 14D) fully engage the top printing plate 18 in a stack of printing plates 20. The remaining suction cups 14A, 14B, 14E, and 14F, do not fully engage the top printing plate 18 and remain open to the atmosphere. As such, due to substantial vacuum leakage through the open suction cups 14A, 14B, 14E, and 14F, there is often insufficient remaining vacuum generated at suction cups 14C and 14D to enable the smaller printing plate 18 to be picked up and held by the vacuum system 10.
To accommodate a variety of different size printing plates, and to avoid the vacuum leakage problems detailed above, available vacuum systems often employ a manifold-type vacuum system, wherein a manifold is configured to selectively apply a vacuum to a plurality of suction cups based on the size of the printing plate to be picked up. Although quite effective, such manifold-type vacuum systems typically have a complex structure, and are expensive to implement, operate, and maintain.
A need therefore exists for simple and inexpensive vacuum system, such as the vacuum system illustrated in FIG. 1, that is capable of picking various size printing plates while controlling the leakage flow through the suction cups that do not engage a printing plate during the picking process.
The present invention provides an apparatus and method for picking printing plates from a stack of printing plates.
Generally, the present invention provides an apparatus, comprising:
a vacuum system including a vacuum source and plurality of suction cups coupled to the vacuum source, wherein at least one of the suction cups is coupled to the vacuum source using a non-constricted fitting, and wherein at least one of the suction cups is coupled to vacuum source using a fixed orifice fitting; and
a stack of printing plates;
wherein the vacuum system is configured to pick a top printing plate from the stack of printing plates, and wherein each suction cup coupled to the vacuum source using a non-constricted fitting is configured to always engage the top printing plate.
The present invention also provides a method, comprising:
providing a vacuum system including a vacuum source and plurality of suction cups coupled to the vacuum source;
coupling at least one of the suction cups to the vacuum source using a non-constricted fitting;
coupling at least one of the suction cups to the vacuum source using a fixed orifice fitting; and
picking a top printing plate from a stack of printing plates using the vacuum system, wherein each suction cup coupled to the vacuum source using a non-constricted fitting is configured to always engage the top printing plate.
The present invention further provides a method for picking and holding an object, comprising:
providing a vacuum system including a vacuum source and plurality of suction cups coupled to the vacuum source;
coupling at least one of the suction cups to the vacuum source using a non-constricted fitting;
coupling at least one of the suction cups to the vacuum source using a fixed orifice fitting; and
picking and holding an object using the vacuum system, wherein each suction cup coupled to the vacuum source using a non-constricted fitting always engages and holds the object, wherein zero or more of the suction cups coupled to the vacuum source using a fixed orifice fitting engage and hold the object, and wherein vacuum leakage through any suction cups that do not engage the object does not substantially affect a vacuum level within the suction cups that do engage the object.